Kombu is dropping Python 3.7 support in their upcoming 5.3 releases,

which are available on PyPI right now as pre-releases. When installing

Review Bot via eggs, easy_install doesn't know to avoid pre-releases

(or to consider supported Python version metadata), so we have to cap

this until we drop support for Python 2.7 and can depend fully on

wheels.
RBTools dropped Python 2.7 and 3.6 in RBTools 4. We had a pretty old

minimum version, so I've taken the opportunity to bump that up. We now

depend on RBTools 3.x for Python 2.7/3.7, and RBTools 4.x or higher for

newer releases.

Successfully installed into new Python 2.7, 3.7, and 3.8 environments.